typedef struct{
    int x;
    int y;
} POINT;

void Input(POINT *p){  scanf("%d%d",&p->x,&p->y);}
void Output(const POINT *p){  printf("(%d %d)",p->x,p->y);}

double Distance(POINT *p,POINT *q){
    int dx=p->x - q->x;
    int dy=p->y - q->y;
    return sqrt(dx * dx + dy * dy);
}

int main(){
    POINT p,q;
    Input(&p);
    Input(&q);
    printf("%.3f\n",Distance(&p,&q));
    return 0;
}
